Helper class for calculating relative scroll offsets in a ListView or GridView by tracking the position of child views.

ListViewScrollTracker.java

  import android.util.SparseArray;
  import android.widget.AbsListView;
  
  /**
   * Helper class for calculating relative scroll offsets in a ListView or GridView by tracking the
   * position of child views.
   */
  public class ListViewScrollTracker {
      private AbsListView mListView;
      private SparseArray<Integer> mPositions;
  
      public ListViewScrollTracker(final AbsListView listView){
          mListView = listView;
      }
  
      /**
       * Call from an AbsListView.OnScrollListener to calculate the incremental offset (change in scroll offset
       * since the last calculation).
       *
       * @param firstVisiblePosition First visible item position in the list.
       * @param visibleItemCount Number of visible items in the list.
       * @return The incremental offset, or 0 if it wasn't possible to calculate the offset.
       */
      public int calculateIncrementalOffset(final int firstVisiblePosition, final int visibleItemCount){
          // Remember previous positions, if any
          SparseArray<Integer> previousPositions = mPositions;
  
          // Store new positions
          mPositions = new SparseArray<Integer>();
          for(int i = 0; i < visibleItemCount; i++){
              mPositions.put(firstVisiblePosition + i, mListView.getChildAt(i).getTop());
          }
  
          if(previousPositions != null){
              // Find position which exists in both mPositions and previousPositions, then return the difference
              // of the new and old Y values.
              for(int i = 0; i < previousPositions.size(); i++){
                  int position = previousPositions.keyAt(i);
                  int previousTop = previousPositions.get(position);
                  Integer newTop = mPositions.get(position);
                  if(newTop != null){
                      return newTop - previousTop;
                  }
              }
          }
  
          return 0; // No view's position was in both previousPositions and mPositions
      }
  
      public void clear(){
          mPositions = null;
      }
  }

perfect

@cnnrhill
Thanks your code :)
Can I use your code in my commercial app?
Please let me know how I can use the code for commercial distribution.